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AT-A-GLANCE

AT-A-GLANCE

  • Dermatomyositis (DM) is a systemic autoimmune disease with a bimodal distribution affecting children and adults, characterized by inflammation and damage to the skin and muscle.

  • Interstitial lung disease (ILD) affects 20% of patients and is a major source of morbidity and mortality in these patients.

  • In adults, DM heralds the diagnosis of a coexisting internal malignancy in 10% to 20% of cases. A thorough review of systems and malignancy workup, including computed tomography scans of the chest, abdomen, and pelvis, may be prudent to detect occult cancers that are missed on routine age-appropriate screening.

  • The diagnosis is established with a combination of the hallmark cutaneous findings and supportive skin histopathology, with or without evidence of a proximal myopathy. The diagnosis may be challenging because 20% of patients never manifest clinically significant muscle weakness.

  • The cutaneous manifestations are typified by violaceous erythema in many sites, most notably the eyelids, upper chest, back, elbows, knees, and lateral hips in addition to proximal nailfold capillary dilation and pericapillary hemorrhage.

  • Characteristic autoantibodies (antisynthetase, anti–Mi-2, anti–transcriptional intermediary factor [TIF1]-γ, anti–melanoma differentiation–associated gene 5 [MDA5], anti–nuclear matrix protein 2 [NXP2], and anti–small ubiquitin-like modifier activating enzyme [SAE] autoantibodies) may be useful in identifying clinical subsets and establishing the diagnosis in cases without the classic clinical or histopathologic features.

  • The presence or absence of certain autoantibodies assists with risk stratification for organ involvement as well as for associated malignancy. Notably, the presence of anti-MDA5 and antisynthetase autoantibodies is associated with an increased risk of ILD, and the presence of anti–TIF1-γ and anti-NXP2 autoantibodies is associated with an increased risk of having an associated cancer.

  • Treatment of cutaneous DM can be challenging, and most patients with significant skin disease require systemic therapy. Multiple agents may be necessary to achieve complete remission; the risks and benefits each agent should be considered carefully given the potentially prolonged treatment course.

INTRODUCTION

DEFINITIONS

Dermatomyositis (DM) continues to be classified as a form of myositis and, in fact, is traditionally considered one of the idiopathic inflammatory myopathies. Implicit in this classification is that myositis is required to make this diagnosis, as well as the characteristic rash—the often used criteria of Bohan and Peter exemplify this.1,2 This is problematic because it is widely accepted now that a proportion of patients, perhaps 20%,3 have the characteristic rash but no clinical signs or symptoms of myositis. These patients make up a population now defined as clinically amyopathic dermatomyositis (CADM), a term coined by Sontheimer in 1991.4 Patients with CADM have the characteristic DM rash (with a consistent skin biopsy) for at least 6 months’ duration but no evidence of weakness by history or clinical examination; earlier concepts also require demonstration of normal muscle enzyme levels,5-7 but this definition was later refined that a patient with normal strength and abnormal muscle enzyme levels could still be included under the ...

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